Researchers at the University of Oxford have found that the risk of a rare type of blood clot is generally low, but higher for people infected with Covid-19 than for people who have had the three UK-approved vaccines – those made by AstraZeneca, Moderna and Pfizer.
The study, made available in print on the Oxford website on Thursday prior to publication in a scientific journal, says the risk of cerebral vein thrombosis or CVT – also known as cerebral venous sinus thrombosis or CVST – after a Covid-19- infection is around. “100 times higher than normal and several times higher than after vaccination or after influenza”, for all age groups.
“Covid-19 clearly increases the risk of CVT and adds to the list of blood clotting problems that this infection causes,” said Paul Harrison, professor of psychiatry and head of the Translational Neurobiology Group at the University of Oxford.
Oxford University, which developed the AstraZeneca vaccine, said the research comes from a separate part of the university and is not affiliated with the vaccine team. The data used was obtained from external sources, in particular the European Medicines Agency.
Compared to the blood clot risk of the three vaccines, the risk of infection is “8-10 times higher, and about 100 times higher for infection compared to baseline,” Oxford said in a press release. According to the study, the risk of CVT from Covid-19 infection is about 10 times greater compared to the mRNA vaccines – Pfizer and Moderna. Compared to AstraZeneca, the risk of CVT from Covid-19 is about eight times greater. The Johnson & Johnson Covid-19 vaccine was not included in the analysis.
Using an electronic patient record network of more than 500,000 Covid-19 positive cases, 489,871 vaccinated cases, and 172,724 cases of influenza, the study found that 30% of CVT cases occurred in the age group under 30, the greatest risk of developing blood clots.
“Given the balance between risks and COVID-19, the risk is higher than with current vaccines, even for people under 30; something to consider when balancing the risk / benefit balance for vaccination, ”Harrison added.
Dr. Maxime Taquet of the Translational Neurobiology Group in Oxford and a co-author of the study cautioned that data is still being collected. Researchers also have yet to determine whether Covid-19 and vaccines similarly lead to CVT, she said.
Experts noted that CVT is so rare that there is limited data even from before the pandemic, and the data and data sources surrounding the Covid-19 vaccines are inconsistent and limited.
“Overall, the main finding is that these CVT events are very rare – a few in every million people involved – in Covid-19 patients and in people who had one of the vaccines – but they were much rarer in the people who had received a vaccine. than in people who had Covid-19, ”said Kevin McConway, professor emeritus of applied statistics at the Open University, in a comment to the Science Media Center in the UK. The researchers do not claim that vaccines do not increase the risk at all compared to the risk in people who have not been vaccinated and also have not had Covid-19 – but they say that the risk of CVT in people who have had Covid-19 is about 100 times the risk in the general population. “
Some background information: European and UK drug regulators last week announced a “possible link” between the AstraZeneca vaccine and rare cases of blood clots, with the UK announcing that it would offer an alternative vaccine to people under 30. Other countries have followed suit, offering either only to people over a certain age or, such as Denmark and Norway, are dropping the vaccine entirely. While advising the public to watch for the signs of blood clots, regulators said the benefits of the injection were still worth the risk. The AstraZeneca vaccine is not approved for use in the United States.
Six reports of similar clotting events following single-dose vaccination with the Johnson & Johnson vaccine prompted the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration to recommend a break from vaccine administration to enable further investigation.
Six women between the ages of 18 and 48 had developed cerebral sinus vein thrombosis, a clot in the area of the brain that collects and drains oxygen-deficient blood. Blood thinners, the typical treatment for blood clots, should not be used in such cases. The six reported cases belonged to more than 6.8 million doses of the Johnson & Johnson vaccine administered in the United States.
The EU, which relies heavily on the J&J vaccine to support the lagging rollout of vaccinations, has also discontinued use of the injection. The European Medicines Agency is expected to issue a decision next week on administering the Johnson & Johnson vaccine.
The WHO said Thursday “for now, the risk of blood clots is much higher for someone with COVID-19 than for someone who has taken the AstraZeneca vaccine.” WHO regional director Hans Kluge reiterated his recommendation of the AstraZeneca vaccine for all eligible adults, calling it “effective in reducing COVID-19 hospitalizations and preventing deaths.”